A. Field of the Invention
The present invention relates to fasteners for anchoring objects to concrete bodies such as pediments and precast concrete walls. More particularly, the invention relates to a novel anchor bolt fastener for installation in precast and poured concrete structures, a novel tool and method for cutting a specially shaped hole in hardened concrete which is adapted to receive the novel fastener and a method for installing the fastener in the hole.
B. Description of Background Art
there are a wide variety of applications in which it is necessary to install a fastener in a concrete structure after the concrete has been poured and hardened. For example bolts or threaded studs protruding perpendicularly from a concrete pediment, base or wall are installed to support vertically disposed street light standards, power poles or the like, or horizontally disposed structures such as floor beams or posts.
Typical prior art fasteners used for installation in concrete bodies such as a pre-cast pediment or wall are expansion-type fasteners which-include an elongated tubular sleeve that has longitudinally disposed slots which extend upwardly from the lower annular end wall of the sleeve, the slots forming therebetween circumferentially spaced apart, longitudinally disposed legs. The shank of an inverted externally threaded stud or bolt which has a rounded head of larger diameter than a bore disposed longitudinally through the sleeve extends upwardly through the bore and protrudes outwardly from the upper annular end wall of the sleeve. The upper threaded end of the stud or bolt shank also protrudes through a circular washer and is threadably received in a hexagonal nut.
Expansion-type concrete anchor bolt fastener of the type described are installed in a concrete body by first boring perpendicularly into an outer face of the body a circular cross-section hole which has a diameter slightly greater than the head of the stud or bolt located at the lower end of the sleeve. The anchor bolt is inserted into the hole bored into the concrete body with the lower surface of a bearing washer seated on the outer flat surface of the concrete body. The hex nut is then tightened onto the threaded shank of the stud or bolt, thus drawing the head at the bottom of the bolt upwards. Upward tension exerted on the bolt shank causes the rounded bolt head to press upwardly against and enter the lower entrance opening of the sleeve bore, causing lower ends of longitudinally disposed legs of the sleeve to expand radially outward and thus exert radially outwardly directed frictional gripping forces on the inner circumferential wall surface of the concrete bore hole. When the hex nut on the upper end of the bolt shank is tightened sufficiently, a substantial frictional force is exerted on the concrete bore wall by the expanded sleeve legs. Thus, the sleeve and bolt are anchored against being withdrawn from the concrete bore hole by substantial frictional forces exerted by the outer surfaces of the sleeve legs on the concrete bore hole wall surface.
Although prior art expansion type concrete anchor bolt fasteners of the type described above are reasonably effective, the uniform diameter of a concrete bore hole in which the anchor bolt sleeve is installed does not have any abutting surfaces which positively resist tensional forces exerted on the upper end of the bolt that could pull the bolt upwards in the bore hole. Therefore, such prior art concrete anchor bolts can and sometimes do work free from their anchored location in a concrete support structure, and are therefor problematic. The present invention was motivated in part by the desire to provide a more securely retainable concrete anchor bolt fastener.